1. Field of the Invention
This invention relates to a downhole tubing connector, and in particular to an arrangement for ensuring the integrity of a sand screen or other filter medium at a connection between two lengths of expandable tubing utilised to support or form a sand screen or filter. The invention also relates to methods of coupling expandable tubing sections together.
2. Description of the Related Art
In many well bores where a liquid, for example oil, passes from a surrounding formation into the well bore, the liquid will often carry entrained sand particles. If this sand is permitted to pass into the well bore a number of problems may arise, including the requirement to separate the sand from produced well fluids; an increased likelihood of the well bore becoming blocked or restricted; and the sand may cause downhole tools to stick or jam, or wear prematurely. Accordingly, it is preferred that the sand particles are retained in the formation. This is achieved by providing screens or a filter around the borehole-lining tubing or production tubing.
International Patent Application No. WO 97/17524 (Shell), the disclosure of which is incorporated herein by reference, describes a radially expandable assembly in which overlapping filter sheets are sandwiched between inner expandable support tubing and outer expandable protective tubing, the expandable tubing featuring large numbers of overlapping longitudinal slots. When an expansion tool is forced through the assembly, the inner and outer tubing is expanded radially, the slots extending to form diamond-shaped openings. The initial degree of overlap between the screens is selected such that, although the screens move circumferentially relative to one another during expansion, the edges of the screens remain in overlapping relation. Such an arrangement can be readily constructed over cylindrical sections of slotted tubing or pipe. However, at the connections between tubing sections, where the inner tubing sections are coupled together, it is difficult to maintain a “sand-tight” join.
A proposed connector assembly for connecting expandable slotted tubing is disclosed in the Applicant's earlier International Patent Publication No. WO96/37681. The connector assembly comprises tubular first and second slotted parts mounted on the ends of respective lengths of slotted tubing. The free end of the first part defines a male portion and the free end of the second part a female portion, the free ends engaging one another to permit expansion of the coupled parts in a corresponding manner to the slotted tubing.
A modified tubing connection arrangement is disclosed in the Applicant's International Patent Publication No. WO00/08301, suitable for coupling expandable tubing assemblies of the type disclosed in WO97/17524. The connection arrangement comprises two expandable tubing sections, each section including a filter screen sandwiched between inner and outer expandable tubing. The filter screen of one tubing section overlaps the filter screen of the other tubing section and the outer expandable tubing of at least one of the tubing sections extends over the overlapping filter screens. On expansion of the tubing sections, the overlapping filter screens, restrained by the outer tubing, ensure the integrity of the filter between the tubing sections.
It is amongst the objects of embodiments of the present invention to provide an improved connection arrangement.